Spontaneous zygogenesis, a wide-ranging mating process in bacteria

Spontaneous zygogenesis (or Z-mating) in Escherichia coli, unlike F-mediated conjugation, promotes formation of complete zygotes. Most Z-mating products have proven to be phenotypically unstable, losing part of the phenotype for which they were selected. Persistent Z-mating products appear as stable genetic recombinants or yield subclones of two types: either both parental types or one of them plus a recombinant type, and the ability to promote spontaneous zygogenesis can appear in all emerging types. Here it is shown that spontaneous zygogenesis-promoting E. coli strains can Z-mate with strains of Shigella flexneri, Salmonella enterica Serovar Typhimurium and Serratia marcescens, giving rise to products that behave like those of homospecific Z-matings. When genetic recombination was prevented in products of Z-mating between E. coli and S. enterica or S. marcescens, phenotype switching was observed in purified isolates exhibiting a single phenotype, thus providing further evidence of interspecies genotypic mixing. The presence of two distinct replicons within a cell introduces a new situation that contrasts with classical conjugation between heterologous strains, where the partially transferred chromosomal segment is subject to restriction, is unable to replicate and is limited in genetic recombination.